Antennas continue to have increasingly strict performance requirements as the communications technology development continues. Especially, the mobile industry continues to develop new techniques to improve the data rate of the mobile devices. This requires the use of new frequencies and wider bandwidths. This means that the antenna must be operated at different frequencies. Obtaining efficient operation over all the required frequencies is challenging, especially with the limited space available for the antennas in the mobile device.
An antenna of a mobile device does not have to function at all operating frequencies simultaneously, making it possible to circumvent the bandwidth requirements via frequency reconfigurability. Instead of covering all the operating frequencies simultaneously, only the required bands are covered at a time.
Existing antenna arrangements which provide frequency re-configurability include matching networks with tunable capacitors and switchable matching networks. These antenna arrangements have separate matching circuits for the separate frequency bands, and the matching circuit is selected via switching. Multiple matching networks require lots of space on the circuit board. They also introduce power losses to the system. Furthermore, there are no matching networks that tune both low and high frequency bands independently. Independent tuning is needed for realizing intra-band carrier aggregation. Alternatively, the antenna element itself can be made reconfigurable by modifying the antenna geometry. Positive Intrinsic Negative (PIN) diodes are commonly used to redirect the flow of the currents in the antenna, therefore modifying the operation.
It is often necessary to fit several antennas on the same mobile device for Multiple-Input and Multiple-Output (MIMO) operation or for different wireless communication systems. Fitting all these antennas on the small device reduces the volume available for a single antenna, which further reduces their bandwidth. This also results in the additional requirement of adequate isolation between the antenna elements. The isolation is often increased via the use of specific decoupling networks. However, existing decoupling networks do not allow tunability of the isolation.